Packer apparatuses

ABSTRACT

A packer apparatus for providing an annular seal in a wellbore is described. The packer apparatus has a body defining a first bore to enable working fluid such as hydraulic fracturing fluid containing proppant to flow through the packer apparatus. A first channel is formed in the body and is arranged to hold hydraulic fluid. A first floating piston is disposed in the first channel, the first floating piston being in fluid communication with the first bore via a passage. A plurality of pistons is arranged to move the activation member relative to the body to deform an elastomeric packer element outwardly relative to the body.

The present invention relates to packer apparatuses for providing annular seals in a wellbore, and relates particularly, but not exclusively, to packer apparatuses for downhole work strings for use in hydraulic fracturing operations to retrieve hydrocarbons from wellbores.

In order to fracture a formation in a hydrocarbon producing wellbore, packer apparatuses are used to isolate and seal sections of the wellbore to enable a working fluid to be pumped at pressure into the formation. The working fluid used in hydraulic fracturing in certain locations requires a proppant material such as sand to be mixed with the working fluid. This ensures effective fracturing in certain types of geological formation.

Inflatable packer apparatuses are known in which rubber elements are inflated into contact with the sides of the wellbore by pumping the working fluid into the rubber element. However, the hydraulic fracturing fluid can be grainy in nature as a result of sand and/or proppant being mixed into the fluid. This can prevent the inflatable packer elements from deflating as a result of resistance of the working fluid to moving out of the inflated packer element.

As a consequence, this can cause the work string to become stuck in a formation which causes both difficulties in retrieving or repositioning the work string and ceases hydrocarbon retrieval. Such a failure is costly and time consuming.

Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.

According to an aspect of the present invention, there is provided a packer apparatus for providing an annular seal in a wellbore, the apparatus comprising:

a body arranged to be disposed in a well bore, the body defining a first bore to enable working fluid to flow through the packer apparatus;

a first channel formed in the body for holding hydraulic fluid;

a first floating piston disposed in the first channel, the first floating piston being in fluid communication with said first bore such that working fluid flowing through the first bore is arranged to cause the first floating piston to move along the first channel to pressurise hydraulic fluid disposed in the first channel;

an activation member mounted to the body, wherein the activation member is moveable relative to the body to deform an elastomeric packer element outwardly relative to the body to form an annular seal in a well bore in use; and

a plurality of pistons arranged to move the activation member relative to the body, each said piston defining a respective pressure chamber being in fluid communication with said first channel such that pressurisation of the hydraulic fluid moves each of the plurality of pistons relative to the body to cause the activation member to move relative to the body to deform the elastomeric packer element outwardly relative to the body.

By providing a first floating piston disposed in a first channel, the first floating piston being able to pressurise hydraulic fluid disposed in the first channel as a result of pumping working fluid through the packer apparatus, this provides the advantage that the activation mechanism for the deformable elastomeric packer element is isolated from the working hydraulic fracturing fluid which might contain sand or another proppant.

This means that sand and other debris is prevented from accumulating in the piston chambers which might cause the packer apparatus to fail and the packer elements to be stuck in the outwardly deformed condition. This helps to ensure that the packer elements retract to the undeformed condition to enable simple retrieval or repositioning of the work string in which the packer apparatus is incorporated.

This also provides the advantage that the packer apparatus can operate at particularly high pressures without a high risk of failure because the mechanical deployment of the packer elements is more reliable than direct inflation. This means that there is a lower risk of packer element failure which consequently reduces the likelihood for leakage and makes the packer apparatus more environmentally friendly.

In a preferred embodiment, said first channel is an annular channel disposed concentrically around the first bore and said first floating piston comprises an annular member disposed in the annular channel.

This provides the advantage that the apparatus can be manufactured by inserting a length of tubing along the first bore to form an annular channel in which in an annular piston can be located. This simplifies and reduces cost of manufacturing as well as providing a compact and reliable arrangement to ensure that sufficient surface area is provided on the floating piston to enable hydraulic fluid pressurisation.

According to another aspect of the present invention, there is provided a work string for use in a wellbore, the work string comprising:

a first packer apparatus as defined above;

a second packer apparatus as defined above; and

a hydraulic fracturing tool connected between said first and second packer apparatuses, the hydraulic fracturing tool comprising:

a second bore connectable to the respective first bores of the first and second packer apparatuses to enable working fluid to flow through the work string; and

at least one nozzle to enable working fluid to flow out of the work string to cause hydraulic fracturing of a formation in which the work string is disposed.

This provides the advantage of a hydraulic fracturing work string that can be run at high pressure whilst providing reliable annular seals to isolate sections of wellbore for high pressure hydraulic fracturing. This reduces leakage and environmental impact, improves hydrocarbon retrieval and reduces the time and cost required to run hydraulic fracturing operations.

This also provides the advantage that the work string operates in a dynamic manner to use the pressure differential between hydraulic fracturing fluid flowing down the work string and the annulus between the work string and the formation to both energise the multiple pistons to deploy the sealing packer elements as well as fracture the formation.

According to a further aspect of the present invention, there is provided a method of hydraulic fracturing a formation to retrieve hydrocarbons, the method comprising:

locating a work string as defined above at a location in a well bore at which a hydraulic fracturing operation is to be conducted; and

pumping working fluid through the work string to:

i. deform the elastomeric packer elements of each said packer apparatus outwardly relative to the work string to form two annular seals in the well bore and form an isolated section of well bore located between the two respective annular seals; and

ii. cause working fluid to be exhausted from the work string through said at least one nozzle into the isolated section of well bore to cause hydraulic fracturing of the formation at the location of the isolated section of well bore.

This provides the advantage of a method of hydraulic fracturing that involves simply locating a work string at a position at which hydraulic fracturing is to be conducted and commencing pumping. Many known methods of hydraulic fracturing require the work string to be manipulated by rotation or reciprocation to deploy the annular packer elements to provide seals. This step is removed in the present method and the only operation required at the surface is to commence and monitor pumping. This significantly reduces the cost and complexity of hydraulic fracturing operations. This also simplifies retrieval and repositioning of the work string.

This also provides the advantage that the method works in a dynamic manner to use the pressure differential between hydraulic fracturing fluid flowing down the work string and the annulus between the work string and the formation to both energise the multiple pistons to deploy the sealing packer elements as well as fracture the formation. This simplifies work string operation for the user.

According to a further aspect of the present invention, there is provided a packer apparatus for providing an annular seal in a well bore, the apparatus comprising:

a body arranged to be disposed in a well bore, the body defining a third bore for holding hydraulic fluid;

a second floating piston disposed in the third bore such that working fluid pumped into said third bore causes the second floating piston to move along the third bore to pressurise hydraulic fluid disposed in the third bore;

an activation member mounted to the body, wherein the activation member is moveable relative to the body to deform at least one elastomeric packer element outwardly relative to the body to form an annular seal in a well bore in use; and

a plurality of pistons arranged to move the activation member relative to the body, each said piston defining a respective pressure chamber being in fluid communication with said third bore such that pressurisation of the hydraulic fluid moves each of the plurality of pistons relative to the body to cause the activation member to move relative to the body to deform said at least one elastomeric packer element outwardly relative to the body.

This provides the advantage of a packer apparatus that can be used at the bottom end of a work string to provide a reliable seal at the base of work string. This packer apparatus is particularly reliable in view of the fact that hydraulic fracturing fluid containing sand or another proppant is prevented from entering the mechanical actuation mechanism for the expandable packer element.

According to a further aspect of the present invention, there is provided a work string for use in a wellbore, the work string comprising:

a first packer apparatus as defined above;

a third packer apparatus as defined above; and

a hydraulic fracturing tool connected between said first and third packer apparatuses, the hydraulic fracturing tool comprising:

a fourth bore connectable to the first bore of the first packer apparatus and the third bore of the third packer apparatus; and

at least one nozzle to enable working fluid to flow out of the work string to cause hydraulic fracturing of a formation in which the work string is disposed.

This provides the advantage of a hydraulic fracturing work string that isolates the mechanical moving parts required to deploy the packer elements from the working fluid, but also prevents fracturing fluid from exiting the bottom of the work string. This reduces leakage and environmental impact, improves hydrocarbon retrieval and reduces the time and cost required to run hydraulic fracturing operations.

This also provides the advantage that the work string operates in a dynamic manner to use the pressure differential between hydraulic fracturing fluid flowing down the work string and the annulus between the work string and the formation to both energise the multiple pistons to deploy the sealing packer elements as well as fracture the formation.

According to a further aspect of the present invention, there is provided a method of hydraulic fracturing a formation to retrieve hydrocarbons, the method comprising:

locating a work string according to claim 6 at a location in a well bore at which a hydraulic fracturing operation is to be conducted; and

pumping working fluid through the work string to:

i. deform the elastomeric packer elements of each said packer apparatus outwardly relative to the work string to form two annular seals in the well bore and form an isolated section of well bore located between the two respective annular seals; and

ii. cause working fluid to be exhausted from the work string through said at least one nozzle into the isolated section of well bore to cause hydraulic fracturing of the formation at the location of the isolated section of well bore.

This provides the advantage of a method of hydraulic fracturing that involves simply locating a work string at a position at which hydraulic fracturing is to be conducted and commencing pumping. Many known methods of hydraulic fracturing require the work string to be manipulated by rotation or reciprocation to deploy the annular packer elements to provide seals. This step is removed in the present method and the only operation required at the surface is to commence and monitor pumping. This significantly reduces the cost and complexity of hydraulic fracturing operations.

This also provides the advantage that the method works in a dynamic manner to use the pressure differential between hydraulic fracturing fluid flowing down the work string and the annulus between the work string and the formation to both energise the multiple pistons to deploy the sealing packer elements as well as fracture the formation. This simplifies work string operation for the user.

Preferred embodiments of the present invention will now be described, by way of example only, and not in any limitative sense, with reference to the accompanying drawings in which:

FIG. 1a is a perspective view of a packer apparatus of a first embodiment of the present invention;

FIG. 1b is a cross-sectional view of the packer apparatus of FIG. 1a shown with the elastomeric packer element in the inactivated undeformed condition;

FIG. 1c is a cross-sectional view of the packer apparatus of FIGS. 1a and 1b showing the elastomeric packer element in the outwardly deformed activated condition;

FIG. 2a is a perspective view of a packer apparatus of a second embodiment of the present invention;

FIG. 2b is a cross-section view of the packer apparatus of FIG. 2a showing the elastomeric packer element in the undeformed deactivated condition;

FIG. 2c is a cross-sectional view of the packer apparatus of FIGS. 2a and 2b showing the elastomeric packer element in the outwardly deformed activated condition;

FIGS. 3a, 4a, 5a, 6a and 7a are longitudinal cross sectional drawings showing a work string embodying the present invention from top to bottom, the upper most portion of the work string being shown in FIG. 3a and moving sequentially downwardly through FIGS. 4a, 5a, 6a to the lower most portion of the work string shown in FIG. 7a , the work string of FIGS. 3a to 7a being shown with the packer elements in the undeformed deactivated condition as a result of no hydraulic fracturing fluid being pumped at pressure down the work string;

FIGS. 3b, 4b, 5b, 6b and 7b are longitudinal cross sectional drawings showing the work string of FIGS. 3a to 7a with the hydraulic packer elements in the outwardly deployed activated condition as a result of hydraulic fracturing fluid being pumped at pressure down the work string;

FIG. 8a is a cross sectional view of a bottom end of a hydraulic fracturing work string incorporating an alternative example of the packer of FIGS. 2a and 2b with the two elastomeric packer elements in the deactivated condition; and

FIG. 8b is a cross-section view of corresponding to FIG. 8a showing the elastomeric packer elements in the activated conditions.

Referring to FIGS. 1a to 1 c, a packer apparatus 2 of a first embodiment of the present invention for providing an annular seal in a wellbore is shown. The packer apparatus 2 comprises a body 4, the body 4 defining a first bore 6 to enable working fluid such as hydraulic fracturing fluid containing sand and/or proppant to flow through the packer apparatus 2.

A first channel 8 is formed in the body and is arranged to hold hydraulic fluid. A first floating piston 10 is disposed in the first channel, the first floating piston being in fluid communication with the first bore 6 via passage 12 such that working fluid flowing through first bore 6 is arranged to cause the first floating piston to move along the first channel 8 to pressurise hydraulic fluid disposed in the first channel 8.

An activation member 14 is mounted to the body. The activation member is moveable relative to the body 4 to deform an elastomeric packer element 16 outwardly relative to the body 4 to form an annular seal in a wellbore in use. The outwardly deformed condition of the elastomeric packer element 16 is shown in FIG. 1c where it can be seen that activation member 14 has advanced to the left of the drawing from the condition shown in FIG. 1 b.

A plurality of pistons 18 are arranged to move the activation member 14 relative to the body 4. Each piston 18 defines a respective pressure chamber 20 being in fluid communication via plurality of ports 22 with the first channel 8. Pressurisation of the hydraulic fluid in first channel 8 therefore moves each of the plurality of pistons 18 relative to the body to cause the activation member 14 to move relative to the body 4 to deform the elastomeric packer element outwardly relative to the body.

The first channel 8 is an annular channel disposed concentrically around the first bore 6. The first floating piston 10 is an annular member located in the annular channel 8. The first channel 8 can be formed by disposing a length of tubing 24 in first bore 6 to create an annular passage in fluid communication with ports 22. In this way, the ports 22 and pressure chambers 20 can be isolated by the first floating piston 10 from hydraulic fracturing fluid flowing in first bore 6.

Consequently, when hydraulic fracturing fluid is pumped along first bore 6, the hydraulic fracturing fluid flows through passage 12 and bears against one side of first floating piston 10. This pushes first floating piston 10 along first travel 8 to pressurise the hydraulic fluid disposed in the first channel 8 and pressure chambers 20. This forces the activation member and pistons 18 to move leftwardly in the drawings and deform elastomeric packer element 16 outwardly. When pumping from the surface is stopped, force on the first floating piston 10 is removed which enables the packer element 16 to move back to the undeformed position and enables removal from or repositioning of the packer apparatus 2 in a well bore.

Referring to FIGS. 2a to 2c , a second embodiment of a packer apparatus according to the present invention is shown. Packer apparatus 42 is arranged to provide an annular seal in a wellbore. Packer apparatus 42 comprises a body 44 arranged to be disposed in a wellbore, the body defining a third bore 46 for holding hydraulic fluid. A second floating piston 50 is disposed in the third bore such that working fluid such as hydraulic fracturing fluid containing a proppant such as sand pumped into the upper end 57 of the third bore 46 bears against second floating piston 50 and causes the second floating piston 50 to move along the third bore 46 to pressurise hydraulic fluid disposed in the third bore.

An activation member 54 is mounted to the body 44 and is moveable relative to the body to deform an elastomeric packer element 56 outwardly relative to the body 44 to form an annular seal in a wellbore in use. A plurality of pistons 58 is arranged to move the activation member 54 relative to the body, each piston 58 defining a respective pressure chamber 60 being in fluid communication via ports 62 with the third bore. As a consequence, pressurisation of hydraulic fluid in first bore 46 and pressure chambers 60 moves each of the plurality of pistons 58 relative to the body to cause the activation member to move relative to the body to deform elastomeric packer element 56 outwardly relative to the body 44.

Packer apparatus 42 is intended to be placed at the bottom end of a work string and therefore the lowermost point in a wellbore in which hydraulic fracturing is being conducted. Since no through flow is required for hydraulic fracturing fluid, the second floating piston 50 is disposed in the central bore 46 of the packer.

Referring to FIGS. 3 to 7, a work string incorporating the packer apparatuses of FIGS. 1 and 2 will now be described to explain the use of the different packer apparatuses 2 and 42 in a work string to conduct hydraulic fracturing in a geological formation. The drawings sequentially from left to right show the work string from top to bottom.

Referring to FIGS. 3a and 3b , the upper most part of the work string 100 is arranged to be located in a wellbore (not shown) on which hydraulic fracturing is to be conducted. This involves pumping hydraulic fracturing fluid which may contain sand or another proppant against the walls of the wellbore to fracture the rock formation in which the wellbore has been drilled to retrieve hydrocarbons in a manner that will be familiar to persons killed in the art.

In this operation, it is necessary to isolate sections of the wellbore. As a consequence, first packer 2 a is disposed in the work string and comprises first elastomeric packer element 16 a. First packer apparatus 2 a is identical to that of the embodiment of FIGS. 1a to 1c and the elastomeric packer element 16 a is expanded outwardly into the condition shown in FIG. 3b against the wall of a wellbore in use as a result of pumping hydraulic fracturing fluid along first bore 6 which moves first floating piston 10 downwardly (to the right in the drawing) to cause deformation of the elastomeric packer element 16 a as described in connection with the embodiment of FIGS. 1a to 1 c.

Connected to the lower end of first packer apparatus 2 a is first hydraulic fracturing tool 102 a which in an example of the present invention is a nozzle stimulation sub. Hydraulic fracturing tool 102 a comprises a second bore 106 a connected to first bore 6 and at least one nozzle 130 a which enables hydraulic fracturing fluid flowing along bores 6 and 106 a to exit the work string 100 and be directed against the formation in the wellbore in which the work string 100 is located. As a result, it can be seen that pumping hydraulic fracturing fluid along the work string 100 both deploys elastomeric packer element 16 a outwardly and causes working fluid to flow out of nozzles 130 a. This dynamic action is advantageous because it utilises the pressure differential between hydraulic fracturing fluid flowing down the work string 100 and the annulus between the work string and the formation (not shown) to both energise the multiple pistons 18 to deploy the sealing packer elements 16 a as well as fracture the formation. This simplifies work string operation for the user.

Referring to FIGS. 4a and 4b , a second packer apparatus 2 b identical to that described in the embodiment of FIGS. 1a to 1 c is connected to the lower end of first hydraulic fracturing tool 102 a. As a consequence, an isolated section of wellbore is formed between first elastomeric packer element 16 a and second elastomeric packer element 16 b when the respective elastomeric packer elements are expanded outwardly against the surface of the wellbore in the conditions of FIGS. 3b and 4 b.

Referring to FIGS. 5a, 6a, 7a, 5b, 6b and 7b , a second isolated section of wellbore is formed, and therefore a second stage of fracturing is enabled using the same workstring 100, between the elastomeric packer elements 16 c of third packer apparatus 2 c (which is identical to that of the embodiment of FIGS. 1a to 1c ) and elastomeric packer element 56 of fourth packer apparatus 42 which is identical to that of the embodiment of FIGS. 2a to 2c . In the isolated section of wellbore between packer elements 16 c and 56, a second hydraulic fracturing apparatus 102 b is disposed to conduct hydraulic fracturing.

It can therefore be seen that with this work string multiple stages of hydraulic fracturing can be conducted whilst still isolating the mechanical moving parts of the work string from hydraulic fracturing fluid which contains sand or proppant and can therefore cause the mechanical elements to fail. Redundancy can be built into the system by using multiple packer apparatuses should one of the annular seals fail. For example, referring to FIGS. 8a and 8b , the lowermost packer apparatus 42 could have more than one elastomeric packer element 56. It has been found that a single floating piston 50 can be used to operate two sets of plural pistons 58 a and 58 b because there is enough volume of hydraulic fluid and travel on the floating piston 50 the energise both the lower packers 56. By the use of multiple chambers, this apparatus has been found to be particularly effective at sealing in very high pressure environments.

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. 

1. A packer apparatus for providing an annular seal in a well bore, the apparatus comprising: a body arranged to be disposed in a well bore, the body defining a first bore to enable working fluid to flow through the packer apparatus; a first channel formed in the body for holding hydraulic fluid; a first floating piston disposed in the first channel, the first floating piston being in fluid communication with said first bore such that working fluid flowing through the first bore is arranged to cause the first floating piston to move along the first channel to pressurise hydraulic fluid disposed in the first channel; an activation member mounted to the body, wherein the activation member is moveable relative to the body to deform an elastomeric packer element outwardly relative to the body to form an annular seal in a well bore in use; and a plurality of pistons arranged to move the activation member relative to the body, each said piston defining a respective pressure chamber being in fluid communication with said first channel such that pressurisation of the hydraulic fluid moves each of the plurality of pistons relative to the body to cause the activation member to move relative to the body to deform the elastomeric packer element outwardly relative to the body.
 2. An apparatus according to claim 1, wherein said first channel is an annular channel disposed concentrically around the first bore and said first floating piston comprises an annular member disposed in the annular channel.
 3. A work string for use in a wellbore, the work string comprising: a first packer apparatus according to claim 1; a second packer apparatus according to claim 1; and a hydraulic fracturing tool connected between said first and second packer apparatuses, the hydraulic fracturing tool comprising: a second bore connectable to the respective first bores of the first and second packer apparatuses to enable working fluid to flow through the work string; and at least one nozzle to enable working fluid to flow out of the work string to cause hydraulic fracturing of a formation in which the work string is disposed.
 4. A method of hydraulic fracturing a formation to retrieve hydrocarbons, the method comprising: locating a work string according to claim 3 at a location in a well bore at which a hydraulic fracturing operation is to be conducted; and pumping working fluid through the work string to: i. deform the elastomeric packer elements of each said packer apparatus outwardly relative to the work string to form two annular seals in the well bore and form an isolated section of well bore located between the two respective annular seals; and ii. cause working fluid to be exhausted from the work string through said at least one nozzle into the isolated section of well bore to cause hydraulic fracturing of the formation at the location of the isolated section of well bore.
 5. A packer apparatus for providing an annular seal in a well bore, the apparatus comprising: a body arranged to be disposed in a well bore, the body defining a third bore for holding hydraulic fluid; a second floating piston disposed in the third bore such that working fluid pumped into said third bore causes the second floating piston to move along the third bore to pressurise hydraulic fluid disposed in the third bore; an activation member mounted to the body, wherein the activation member is moveable relative to the body to deform at least one elastomeric packer element outwardly relative to the body to form an annular seal in a well bore in use; and a plurality of pistons arranged to move the activation member relative to the body, each said piston defining a respective pressure chamber being in fluid communication with said third bore such that pressurisation of the hydraulic fluid moves each of the plurality of pistons relative to the body to cause the activation member to move relative to the body to deform said at least one elastomeric packer element outwardly relative to the body.
 6. A work string for use in a wellbore, the work string comprising: a first packer apparatus for providing an annular seal in a well bore, the first packer apparatus comprising: a body arranged to be disposed in a well bore, the body defining a first bore to enable working fluid to flow through the packer apparatus; a first channel formed in the body for holding hydraulic fluid; a first floating piston disposed in the first channel, the first floating piston being in fluid communication with said first bore such that working fluid flowing through the first bore is arranged to cause the first floating piston to move along the first channel to pressurize hydraulic fluid disposed in the first channel; an activation member mounted to the body, wherein the activation member is moveable relative to the body to deform an elastomeric packer element outwardly relative to the body to form an annular seal in a well bore in use; and a plurality of pistons arranged to move the activation member relative to the body, each said piston defining a respective pressure chamber being in fluid communication with said first channel such that pressurisation of the hydraulic fluid moves each of the plurality of pistons relative to the body to cause the activation member to move relative to the body to deform the elastomeric packer element outwardly relative to the body; a third packer apparatus for providing an annular seal in a well bore, the third packer apparatus comprising: a body arranged to be disposed in a well bore, the body defining a third bore to enable working fluid to flow through the packer apparatus; a second floating piston disposed in the third bore, such that working fluid pumped into said third bore causes the second floating piston to move along the third bore to pressurize hydraulic fluid disposed in the third bore; an activation member mounted to the body, wherein the activation member is moveable relative to the body to deform at least one elastomeric packer element outwardly relative to the body to form an annular seal in a well bore in use; and a plurality of pistons arranged to move the activation member relative to the body, each said piston defining a respective pressure chamber being in fluid communication with said first channel such that pressurisation of the hydraulic fluid moves each of the plurality of pistons relative to the body to cause the activation member to move relative to the body to deform said at least one elastomeric packer element outwardly relative to the body; and a hydraulic fracturing tool connected between said first and third packer apparatuses, the hydraulic fracturing tool comprising: a fourth bore connectable to the first bore of the first packer apparatus and the third bore of the third packer apparatus; and at least one nozzle to enable working fluid to flow out of the work string to cause hydraulic fracturing of a formation in which the work string is disposed.
 7. A method of hydraulic fracturing a formation to retrieve hydrocarbons, the method comprising: locating a work string according to claim 6 at a location in a well bore at which a hydraulic fracturing operation is to be conducted; and pumping working fluid through the work string to: i. deform the elastomeric packer elements of each said packer apparatus outwardly relative to the work string to form two annular seals in the well bore and form an isolated section of well bore located between the two respective annular seals; and ii. cause working fluid to be exhausted from the work string through said at least one nozzle into the isolated section of well bore to cause hydraulic fracturing of the formation at the location of the isolated section of well bore.
 8. A work string for use in a wellbore, the work string comprising: a first packer apparatus according to claim 2; a second packer apparatus according to claim 2; and a hydraulic fracturing tool connected between said first and second packer apparatuses, the hydraulic fracturing tool comprising: a second bore connectable to the respective first bores of the first and second packer apparatuses to enable working fluid to flow through the work string; and at least one nozzle to enable working fluid to flow out of the work string to cause hydraulic fracturing of a formation in which the work string is disposed.
 9. A method of hydraulic fracturing a formation to retrieve hydrocarbons, the method comprising: locating a work string according to claim 8 at a location in a well bore at which a hydraulic fracturing operation is to be conducted; and pumping working fluid through the work string to: i. deform the elastomeric packer elements of each said packer apparatus outwardly relative to the work string to form two annular seals in the well bore and form an isolated section of well bore located between the two respective annular seals; and ii. cause working fluid to be exhausted from the work string through said at least one nozzle into the isolated section of well bore to cause hydraulic fracturing of the formation at the location of the isolated section of well bore. 